diff --git a/crates/egui/src/containers/panel.rs b/crates/egui/src/containers/panel.rs
index 2869f598cf4..9478ffe67ae 100644
--- a/crates/egui/src/containers/panel.rs
+++ b/crates/egui/src/containers/panel.rs
@@ -151,6 +151,8 @@ impl SidePanel {
     /// * A [`crate::Separator`].
     /// * A [`crate::TextEdit`].
     /// * …
+    /// If you don't provide an expandable widget, the resize behavior is
+    /// undefined.
     #[inline]
     pub fn resizable(mut self, resizable: bool) -> Self {
         self.resizable = resizable;